Linear alpha-olefins having 4 to 20 carbon atoms are key feedstocks in the production of surfactants, plasticizers, synthetic lubricants, and polyolefins. High purity alpha-olefins are particularly valuable in the production of low density polyethylene and in the oxo process.
The most successful processes for the production of alpha-olefins to date are those catalyzed by nickel complexes of phosphine-carboxylate ligands and sulfonated ylide/nickel type compounds. While these catalysts are quite active and have good selectivity insofar as the production of alpha-olefins is concerned, the art is continuously searching for ethylene oligomerization catalysts, which display higher activity and greater alpha-olefin selectivity and allow for a more economical process.
For example, insofar as economy is concerned, the process utilizing the nickel complexes of phosphine-carboxylate ligands requires three reaction steps; ethylene oligomerization, isomerization of C.sub.20.spsb.+ product, and disproportionation of C.sub.20.spsb.+ internal olefins to C.sub.11 to C.sub.14 internal olefins. The latter two steps are necessary because C.sub.20.spsb.+ olefins have little commercial value. The high level of internal olefin production also raises a problem of purity important, as noted, in the production of low density polyethylene and the oxo process. Other disadvantages of these catalysts follow: the ligands are expensive to prepare; polyethylene formation must be guarded against; the catalysts are relatively unstable; solvent is degraded; and ethylene pressure requirements are high. The sulfonated ylide/nickel type catalysts suffer from similar deficiencies.